Geomagnetic Effects on Heavy Primary Cosmic Radiation at 42°N

The zenith and azimuthal angular distribution of primary cosmic rays with charges Z≥5 has been measured at Texas using horizontal emulsions with known orientation relative to the earth. The magnitude of the azimuthal asymmetry is consistent with St\"ormer theory down to a zenith angle of about 65^∘{} while for larger zenith angles the effect of the solid earth (shadow cone) is observed. The direction of the asymmetry seems to be consistent with the centered dipole approximation of the earth's magnetic field (north pole at 79^∘{}N and 70^∘{}W). The flux at the top of the atmosphere is 1.6±{}0.3 particles/m² sec sterad for nuclei with Z≥10 and 4.8±{}1.0 particles/m² sec sterad for CNOF nuclei.